Order path data in GeomSmooth (tidyverse#2029)

Fixes tidyverse#2028

Author: izahn

NEWS.md

@@ -1,5 +1,8 @@
 # ggplot2 2.2.1.9000
 
+* `geom_smooth` now orders by the `x` aesthetic, making it easier to pass 
+  pre-computed values without manual ordering (@izahn, #2028).
+
 * Fixed bug in `coord_polar` that prevented moving the radius axis
   to the right (@thomasp85, #2005).
 

R/geom-smooth.r

@@ -114,6 +114,9 @@ geom_smooth <- function(mapping = NULL, data = NULL,
 #' @usage NULL
 #' @export
 GeomSmooth <- ggproto("GeomSmooth", Geom,
+  setup_data = function(data, params) {
+    GeomLine$setup_data(data, params)
+  },
   draw_group = function(data, panel_params, coord) {
     ribbon <- transform(data, colour = NA)
     path <- transform(data, alpha = NA)

tests/testthat/test-geom-smooth.R

@@ -0,0 +1,10 @@
+context("geom_smooth")
+
+test_that("Data is ordered by x", {
+  df <- data.frame(x = c(1, 5, 2, 3, 4), y = 1:5)
+
+  ps <- ggplot(df, aes(x, y))+
+    geom_smooth(stat = "identity", se = FALSE)
+
+  expect_equal(layer_data(ps)[c("x", "y")], df[order(df$x), ])
+})